1. Field
Aspects of the present invention generally relate to an ink filling method for filling a sub-tank with ink from a main tank disposed in an inkjet recording apparatus, and an inkjet recording apparatus employing the method.
2. Description of the Related Art
Recently, an ink jet recording apparatus has been used to record various types of images on a large recording medium such as A1 size and A0 size. This type of inkjet recording apparatus generally employs a configuration in which an inkjet recording head (hereinafter referred to as a recording head) mounted on a carriage performing reciprocating scanning in a main scanning direction is connected via a tube to a large-volume main tank (hereinafter referred to a main tank) to supply ink to the recording head.
The large inkjet recording apparatus has a wide range of uses including recording of various types of images from monochrome line drawings to photographic tone images. When the large inkjet recording apparatus records an image having a high printing duty such as a photographic tone image, a large amount of ink is consumed. Although the large-volume main tank is used in the large inkjet recording apparatus, a large amount of ink can be consumed depending on the type of recording image or the volume of printing. The consumption of a large amount of ink causes an increase in frequency of main tank replacement.
When the main tank is connected via the tube to the recording head, a recording operation needs to be stopped to replace the main tank. This decreases the recording efficiency due to a waste of time for replacing the main tank. Moreover, if a recording operation is interrupted in the middle of recording on one recording medium for main tank replacement, the lapse of time causes color unevenness between before and after the interruption and deteriorates image quality.
Accordingly, Japanese Patent Application Laid-Open No. 2010-208151 discusses an inkjet recording apparatus including a sub-tank disposed between a main tank and a recording head so that the main tank can be replaced without interrupting a recording operation. In Japanese Patent Application Laid-Open No. 2010-208151, the main tank is connected to the sub-tank, and ink is moved from the main tank to the sub-tank to fill the sub-tank with the ink. Then, the ink is supplied from the sub-tank to the recording head connected via a tube, so that a recording operation is performed. In such a configuration, even if ink inside the main tank is used up, the inkjet recording apparatus can continue a recording operation using ink stored inside the sub-tank. Thus, the main tank can be replaced while the recording operation is performed using the ink inside the sub-tank. Therefore, the main tank can be replaced without interrupting the recording operation, thereby preventing a decrease in recording efficiency due to a waste of time for replacing the main tank and a deterioration in image quality due to a lapse of time.
In Japanese Patent Application Laid-Open No. 2010-208151, a valve capable of blocking an ink supply flow path is disposed in a middle portion of the tube. The tube serves as the ink supply flow path, and connects the sub-tank to the recording head. This valve includes a volume-changeable member (hereinafter referred to as a diaphragm valve), and the operation of this diaphragm valve can cause negative pressure in the sub-tank. When the sub-tank needs to be filled with ink supplied from the main tank, the diaphragm valve is operated to cause the negative pressure in the sub-tank. This negative pressure enables ink to be pulled into the sub-tank from the main tank.
However, when the diaphragm valve disposed between the sub-tank and the recording head is operated to fill the sub-tank with ink, the ink path connecting the sub-tank to the recording head needs to be repeatedly closed and opened. Consequently, when the diaphragm valve is operated, ink cannot be supplied to the recording head, and thus the inkjet recording apparatus cannot continue the recording operation. That is, the ink filling operation to the sub-tank cannot be performed along with the recording operation. The recording operation is interrupted during the ink filling to the sub-tank since the ink filling operation needs to be performed independently from the recording operation, thereby causing a decrease in the recording efficiency.
Accordingly, inventors of the present invention have studied an inkjet recording apparatus capable of filling a sub-tank with ink from a main tank using dynamic pressure of ink in a tube, the dynamic pressure being generated by the acceleration of a carriage. In the recording apparatus having the main tank and the sub-tank, even when the carriage is not accelerating, the same amount as the amount of ink used for a recording operation (also referred to as a recording ink amount) is supplied from the main tank to the sub-tank. The amount of ink is supplied since the pressure inside the sub-tank is reduced when the ink in the sub-tank is used by the recording operation.
That is, in the recording apparatus studied by the inventors of the present invention, the amount of ink used for recording and the amount of ink moved by using the dynamic pressure are supplied from the main tank to the sub-tank. In terms of the sub-tank only, the amount of ink thereof is increased by the amount of ink moved by the dynamic pressure.
However, in a case where there is not much ink in the main tank to fill the sub-tank with ink by the dynamic pressure, ink in the main tank may become empty before the sub-tank is filled with a sufficient amount of ink. In case of such a situation, an ink shortage may occur during recording of one image, although the recording apparatus has the sub-tank.